Method of preparing organometallic compounds

ABSTRACT

A method of preparing an ultra-pure metal amidinate compound comprising using a microchannel device for synthesis in reacting a metal halide solution with a lithium amidinate solution to produce an ultra-pure alkylmetal compound for processes such as chemical vapor deposition.

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Patent Application No. 60/961,370 filed on Jul. 20,2007 and Non-Provisional Patent Application No. 12215828 filed on Jun.30, 2008.

This invention relates to methods of making organometallic compounds(OMCs). In particular the invention is directed to methods of makingorganometallic compounds of high purity for processes such as chemicalvapor deposition.

Metal films may be deposited on surfaces, such as non-conductive(Electronic materials applications) surfaces, by a variety of means suchas chemical vapor deposition (“CVD”), physical vapor deposition (“PVD”),and other epitaxial techniques such as liquid phase epitaxy (“LPE”),molecular beam epitaxy (“MBE”), chemical beam epitaxy (“CBE”) and atomiclayer deposition (“ALD”). Chemical vapor deposition processes, such asmetalorganic chemical vapor deposition (“MOCVD”), deposit a metal layerby decomposing organometallic precursor compounds at elevatedtemperatures, i.e., above room temperature, either at atmosphericpressure or at reduced pressures. A wide variety of metals may bedeposited using such CVD or MOCVD processes.

For semiconductor and electronic device applications, organometallicprecursor compounds must be ultra pure and be substantially free ofdetectable levels of both metallic impurities, such as silicon and zinc,as well as other impurities including hydrocarbons and oxygenatedcompounds. Ideally, ultra purity is producing materials with level ofimpurities <0.1 wt %, preferably <1 ppm, or even <1 ppb. Oxygenatedimpurities are typically present from the solvents used to prepare suchorganometallic compounds, and are also present from other adventitioussources of moisture or oxygen. Achieving ultra purity is important whenmanufacturing materials for electronic applications including Group IIIand V OMCs for CVD to produce compound semi-conductors for LEDs andoptoelectronic devices, or organometallic precursors for ALD to growthin films for advanced silicon chips. Some impurities have similarboiling points in relation to the organometallic precursor compoundsmaking it difficult to achieve high purity with conventionaldistillation technology.

Much work has been done to improve the synthetic methods for makingultra-pure organometallic precursor compounds. Historically,organometallic precursor compounds have been prepared by batch processesbut recently, as disclosed in U.S. Pat. No. 6,495,707 and U.S. PatentPublication No. 2004/0254389, continuous methods for producingorganometallic compounds such as trimethylindium and trimethylgalliumhave become available.

Despite these advances, the synthesis of organometallic compoundsremains difficult. Many of the reactions are exothermic and theproduction of large amounts, particularly with such high purity, isdifficult. In addition it is difficult to scale the production ofmaterials to match fluctuating demand and storage of the organometalliccompounds can be undesirable as impurities and degradation products canbe introduced.

Traditional methods used for purification include distillation,crystallization, adduct purification, mass-selective ultracentrifuge,and chemical treatment combined with distillation. While these methodsprovide some reduction in the level of impurities, there is a continuingneed to produce ultra-pure organometallic compounds to meet theperformance demands of today's most advanced electronic devices.Furthermore, there is often an economic constraint to the purity levelsattainable with existing methods. Excessive capital or operating costscan limit the attainable purity due to unacceptable yield loss, energyinput, or process cycle time due to the physical and/or chemicalproperties of the impurities and the organometallic compound.

For example, it is possible to estimate the minimum number ofequilibrium stages required for distillation based on the relativevolatility (a) of the components and the desired purity using the FenskeEquation. To remove the most problematic, near boiling impurities(a<1.2), the number of stages, or height equivalent theoretical plates(HETP), can exceed 50, 100, or even 200 which can require a columnheight of >10 meters even with today's most advanced packings (HETP=0.05to 0.20 m). A column of this size poses difficult scale-up andoperability challenges and safety concerns from the large inventory ofpyrophoric organometallic compounds, when attempting to make ultra-purematerials.

Accordingly, there is an ongoing need for new methods of preparingultra-pure organometallic compounds for use as CVD precursors.

The present invention meets this foregoing need by drawing upon thebenefits of microchannel devices. Microchannel devices provide bettercontrol of process conditions, improved safety, and speed to market fromlaboratory development to commercial manufacturing. A continuous flowmicro-reactor, one example of a microchannel device, helps achieveimproved synthesis yields and purity through superior heat and masstransfer to control the reaction conditions and minimize the risk of areaction runaway or hazardous spill through low inventory of materials.The microchannel device further enables production scale-up by“numbering-up” multiple devices to meet market demand with noperformance loss and at significant time and cost savings without theneed for traditional process scale-up studies.

Microchannel devices can also be used for separation and purificationsteps of reagents, solvents, intermediates, or final products withsimilar benefits. The basis for the benefits in microchannel technologyarise from the high surface area provided in the device which enableshigh exchange rates between phases. Enhancement of separation isachieved in the microchannel architecture dimensions, typically 1 to1000 microns, through an increased importance of interfacial phenomenaand reduced distances for heat and mass-transfer. The superior heat andmass transfer in these devices provides high exchange rates betweenphases and better temperature control for more efficient separationstages or lower height equivalent theoretical plate (HETP). This enablesmore stages for higher purity in a fixed separation device geometry.There are also benefits in lower capital intensity and lower operatingcosts through improved energy efficiency by better integration of heatexchange.

Microchannel devices can be used in a wide range of separationapplications including distillation, adsorption, extraction, absorption,and gas stripping.

By drawing upon the benefits of microchannel technology, the presentinvention succeeds in producing ultra-pure organometallic precursorcompounds.

In one aspect of the present invention there is provided a process forpreparing organometallic compounds of ultra-high purity comprising:

reacting a metal salt, such as a metal halide, and an alkyating agent,such as an alkyl metal, in a microchannel device to yield anorganometallic compound wherein the resulting compound has the minimumpurity required for chemical vapor deposition processes.

In a second aspect of the present invention there is provided a methodof preparing an organometallic compound of ultra-high purity comprisingpurifying an organometallic compound comprising impurities in amicrochannel device to reduce the level of impurities with relativevolativity (a) between 0.8<a<1.5 to a level useful in electronicmaterials applications.

As used herein, the term “metal halide” refers to a compound containinga metal and at least one halogen bound to the metal. The metal may alsohave additional, non-halide substituents.

As used herein, the term “electronic materials applications” refers toapplications including but not limited to chemical vapor deposition(“CVD”), physical vapor deposition (“PVD”), and other epitaxialtechniques such as liquid phase epitaxy (“LPE”), molecular beam epitaxy(“MBE”), chemical beam epitaxy (“CBE”) and atomic layer deposition(“ALD”). In electronic materials applications, the level of impuritieswith relative volativity (a) between 0.8<a<1.5 typically must be below100 ppm, alternatively below 1 ppm.

“Halogen” refers to fluorine, chlorine, bromine and iodine and “halo”refers to fluoro, chloro, bromo and iodo. Likewise, “halogenated” refersto fluorinated, chlorinated, brominated and iodinated. “Alkyl” includeslinear, branched and cyclic alkyl. Likewise, “alkenyl” and “alkynyl”include linear, branched and cyclic alkenyl and alkynyl, respectively.The term “Group IV metal” is not intended to include Group IV non-metalssuch as carbon. Likewise, the term “Group VI metal” is not intended toinclude Group VI non-metals such as oxygen and sulfur. “Aryl” refers toany aromatic moiety, and preferably an aromatic hydrocarbon.

The articles “a” and “an” refer to the singular and the plural.

As used herein, “CVD” is intended to include all forms of chemical vapordeposition for example: Metal Organic Chemical Vapor Deposition (MOCVD),Metal Organic Vapor Phase Epitaxy (MOVPE), Oganometallic Vapor PhaseEpitaxy (OMVPE), Organometallic Chemical Vapor Deposition (OMCVD) andRemote Plasma Chemical Vapor Deposition (RPCVD). In CVD processesorganometallic compounds must have a purity of at least 99.9999% inorder to meet stringent electrical or optoelectronic performancerequirements of semiconducting devices produced using theseorganometallic compounds.

Unless otherwise noted, all amounts are percent by weight and all ratiosare molar ratios. All numerical ranges are inclusive and combinable inany order except where it is clear that such numerical ranges areconstrained to add up to 100%.

Microchannel devices offer novel opportunities in chemical synthesis andpurification. Microchannel devices have channel cross-section dimensions(widths) of 0.1 to 5,000 micrometers, preferably 1 to 1,000 micrometers,or more preferably, 1 to 100 micrometers. Microchannel devices aretypically comprised of multiple channels for fluid flow in parallel tothe primary flow direction. Due to the small channel cross-sectiondimensions, the microchannel device has a high surface area to volumeratio resulting in highly efficient mass and heat transfer. Inparticular, mass transfer is on the molecular scale and heat transfercoefficients can be up to 25 kilowatts/square meterKelvin or more. Forcomparison, heat transfer coefficients of conventional jacketed reactorsare typically 0.1 to 0.2 kilowatts/square meterKelvin. The highlyefficient mass and heat transfer in a microchannel device permits muchtighter control of reaction conditions such as temperature, reactantconcentration and residence time. Temperature control is particularlyimportant for preparation of high purity organometallic products.Deviations from isothermal conditions for exothermic or endothermicreactions can lead to increased amounts of undesired side productsresulting in lower product yield and purity. Precise temperature controlin the production of high purity products decreases or, in some caseseliminates, the need for subsequent purification, thus decreasing theoverall amount of resources required to produce the organometalliccompound.

As each microchannel device typically produces a small quantity oforganometallic precursor, a number of microchannel devices may be usedin parallel. Total volume produced by the series of microchannel devicescan be controlled by increasing or decreasing the number of microchanneldevices in use at any given point in time, thus decreasing oreliminating the need for product storage.

Microchannel devices may be made from any conventional materialincluding but not limited to metals, polymers, ceramics, silicon orglass. Exemplary metals include but are not limited to metal alloys,such as Hastelloy™ alloys, readily available from Haynes International,Inc., and austenitic stainless steels such as, for example, 304, 312,and 316 stainless steels. Methods of fabrication include but are notlimited to mechanical micro-machining, molding, tape casting, etching,laser patterning, sandblasting, hot embossing, lithography, andmicro-stereolithography. The microchannel device may be constructed withboth smooth channel walls and/or channels with structural features onthe channel walls that enhance heat and mass transfer. A microreactor isone example of a microchannel device.

In some microchannel device embodiments used for conducting reactions,the microreactor comprises an inlet for each reagent. In reactionsemploying three or more reagents, two or more reagents may be combinedand fed to the microreactor via a single inlet with the proviso that thetotal number of reagents is not combined until in the microreactionzone. For example, when the reaction employs three reagents, two of thereagents may be co-fed to the microreactor via the same inlet and thethird reagent may be fed via a second inlet.

The microchannel device can comprise a separate channel system fortemperature control via an external cooling or heating source. Exemplarysystems include, but are not limited to hot oil, hot water, hot steam,cold oil, cold water, cold baths, and refrigeration units. As usedherein, by “hot” is meant temperatures above room temperature, typicallyabove 35° C. As used herein, by “cold” is meant temperatures below roomtemperature, typically below 15° C. In the case of a microreactor, thedevice is operated at a temperature appropriate for the particularsynthesis reactions.

The microchannel device may further comprise a micromixer for mixing ofthe inlet streams.

The microchannel device can have a length ranging from 1 micrometer to 1meter, or greater, depending on the process requirements or the devicefabrication method. Multiple microchannel devices can be usedsequentially if required to achieved the desired overall length. In thecase of a microreactor, the length of the microchannel device isdictated by the kinetics of the particular reaction being performed inaddition to the flow rate and temperature. Slower reactions require alonger residence time in the microreactor and hence a longermicroreactor. Additionally, when sequential reactions are desired themicroreactor can comprise additional inlets along the length of thedevice or between devices for additional reagents.

The microchannel device comprises an outlet for the removal of product.In some embodiments the microchannel device comprises two outlets, onefor a liquid stream and one for a gaseous stream. The product streamsfrom a microreactor may then be subjected to purification, using eitherconventional purification methods, microchannel purification, or acombination thereof.

An example of a microreactor is disclosed in U.S. Pat. No. 6,537,506which describes a stacked plate, multichannel reactor incorporating heattransfer fluid pathways, reactant fluid pathways, product pathways,mixing chambers and reaction chambers.

The microchannel device may optionally contain a wick or membranestructure to control the liquid film thickness and enhance interfacialphenomena. Microchannel devices may be used for fluid separationincluding distillation. The application of microchannel devices to acommercially important distillation application is the C₂ splitter,which separates ethane from ethylene. The microchannel distillationprocess can reduce energy consumption and capital costs for ethyleneproduction.

The present invention provides a process for preparing an organometalliccompound by reacting a metal salt with an alkylating agent in amicrochannel device to produce an ultra-pure alkylmetal compound forprocesses such as chemical vapor deposition. Additionally the alkylatingagents of the present invention may themselves be purified.

Examples of metal salt and alkylating agent combinations include but arenot limited to reacting a metal halide with a trialkylaluminum solution,a metal halide solution with an alkyl magnesium halide, or a metalhalide solution with an alkyl lithium solution in a microchannel device,such as a microreactor, to produce an alkyl metal compound. In someembodiments the molar ratio of alkylating agent to metal salt is greaterthan or equal to one. In some embodiments the molar ratio is greaterthan or equal to 2. In some embodiments the molar ratio is greater thanor equal to 3.

The metal halide may comprise a Group II, Group III, Group IV, or GroupV metal. There are a sufficient number of halogens present in the metalhalide to form a neutral compound. Exemplary metal halides include, butare not limited to, ZnCl₂, GaCl₃, InCl₃, InBr₃, InI₃, GeCl₄, SiCl₄,SnCl₄, PCl₃, AsCl₃, SbCl₃ and BiCl₃.

The trialkylaluminum solution comprises three alkyl groups, which may bethe same or different. Each alkyl group comprises 1 to 8 carbons. Thealkyl groups may be straight chain, branched or cyclic. The alkylmagnesium halide and alkyl lithium compounds comprise a single alkylgroup comprising 1 to 8 carbons. Likewise, the alkyl groups may bestraight chain, branched or cyclic.

The metal salt solution and the alkylating agent solution may compriseany organic solvent which is inert to the reaction between the twoconstituents and is also inert to any products resulting from thereaction. In some embodiments the metal salt solution is free ofsolvent, i.e., the metal salt is already in liquid form and is added“neat”. The solvent should be chosen to provide sufficient solubilityfor the reaction to proceed. The metal salt solution and the alkylatingagent solution may use the same or different solvents. Particularlysuitable organic solvents include, but are not limited to, hydrocarbonsand aromatic hydrocarbons. Exemplary organic solvents include, withoutlimitation, benzene; alkyl substituted benzenes such as toluene, xylene,and (C₄-C₂₀)alkyl benzenes such as (C₁₀-C₁₂)alkyl benzenes and(C₁₀-C₂₀)alkyl biphenyls; and aliphatic hydrocarbons such as pentane,hexane, heptane, octane, decane, dodecane, squalane, cyclopentane,cyclohexane, and cycloheptane; and mixtures thereof. More preferably,the organic solvent is benzene, toluene, xylene, (C₄-C₂₀)alkyl benzenes,hexane, heptane, cyclopentane or cyclohexane. It will be appreciatedthat more than one organic solvent may be advantageously used. Suchorganic solvents are generally commercially available from a variety ofsources, such as Aldrich Chemicals (Milwaukee, Wis.). Such solvents maybe used as is or, preferably, purified prior to use.

Preferably, such organic solvents are dry and deoxygenated prior to use.The solvents may be deoxygenated by a variety of means, such as purgingwith an inert gas, degassing the solvent in vacuo, or a combinationthereof. Suitable inert gases include argon, nitrogen and helium, andpreferably argon or nitrogen.

In an alternative embodiment, ionic liquids will be employed as thesolvents that do not interact with organometallic synthesis underconsideration, and offer “green sovents” that are environment-friendly.Ionic liquids are generally salts that are liquid at low temperatures,having melting points under 100° C. Many ionic liquids remain in theliquid phase at room temperature, and are referred to as roomtemperature ionic liquids. Ionic liquids are composed entirely of ionsand typically they are composed of bulky organic cations and inorganicanions. Due to the high Coulombic forces in these compounds, ionicliquids have practically no vapor pressure.

Any suitable ionic liquid may be employed in the present invention.Exemplary cations used in ionic liquids include, but are not limited to,hydrocarbylammonium cations, hydrocarbylphosphonium cations,hydrocarbylpyridinium cations, and dihydrocarbylimidazolium cations.Exemplary anions useful in the present ionic liquids include, but arenot limited to, chlorometalatc anions, fluoroborate anions such astetrafluoroborate anions and hydrocarbyl substituted fluoroborateanions, and fluorophosphate anions such as hexafluorophosphate anionsand a hydrocarbyl substituted fluorophosphate anions. Examples ofchlorometalate anions include, but are not limited to, chloroaluminateanion such as tetrachloroaluminate anion and a chlorotrialkylaluminateanion, chlorogal late anions such as chlorotrimethylgallate andtetrachlorogallate, chloroindate anions such as tetrachloroindate andchlorotrimethylindate.

Suitable chloroaluminate-based ionic liquids include, withoutlimitation, those having a hydrocarbyl substituted ammonium halide, ahydrocarbyl substituted phosphonium halide, a hydrocarbyl substitutedpyridinium halide, or a hydrocarbyl substituted imidazolium halide.Exemplary chloroaluminate-based ionic liquids include, but are notlimited to, trimethylphenyl ammonium chloroaluminate (“TMPACA”),benzyltrimethyl ammonium chloroaluminate (“BTMACA”), benzyltriethylammonium chloroaluminate (“BTEACA”), benzyltributyl ammoniumchloroaluminate (“BTBACA”), trimethylphenyl phosphonium chloroaluminate(“TMPPCA”), benzyltrimethyl phosphonium chloroaluminate (“BTMPCA”),benzyltriethyl phosphonium chloroaluminate (“BTEPCA”), benzyltributylphosphonium chloroaluminate (“BTBPCA”), 1-butyl-4-methyl-pyridiniumchloroaluminate (“BMPYCA”), 1-butyl-pyridinium chloroaluminate(“BPYCA”), 3-methyl-1-propyl-pyridinium chloroaluminate (“MPPYCA”),1-butyl-3-methyl-imidazolium chloroaluminate (“BMIMCA”),1-ethyl-3-methyl-imidazolium chloroaluminate (“EMIMCA”),1-ethyl-3-methyl-imidazolium bromo-trichloroaluminate (“EMIMBTCA”),1-hexyl-3-methyl-imidazolium chloroaluminate (“HMIMCA”), benzyltrimethylammonium chlorotrimethylaluminate (“BTMACTMA”), and1-methyl-3-octyl-imidazolium chloroaluminate (“MOIMCA”).

Other suitable ionic liquids include those having a fluoroborate anionor a fluorophosphate anion, such as, but not limited to, trimethylphenylammonium fluoroborate (“TMPAFB”), benzyltrimethyl ammonium fluoroborate(“BTMAFB”), benzyltriethyl ammonium fluoroborate (“BTEAFB”),benzyltributyl ammonium fluoroborate (“BTBAFB”), trimethylphenylphosphonium fluoroborate (“TMPPFB”), benzyltrimethyl phosphoniumfluoroborate (“BTMPFB”), benzyltriethyl phosphonium fluoroborate(“BTEPFB”), benzyltributyl phosphonium fluoroborate (“BTBPFB”),1-butyl-4-methyl-pyridinium fluoroborate (“BMPFB”), 1-butyl-pyridiniumfluoroborate (“BPFB”), 3-methyl-1-propyl-pyridinium fluoroborate(“MPPFB”), 1-butyl-3-methyl-imidazolium fluoroborate (“BMIMFB”),1-ethyl-3-methyl-imidazolium fluoroborate (“EMIMFB”),1-ethyl-3-methyl-imidazolium bromo-trifluoroborate (“EMIMBTFB”),1-hexyl-3-methyl-imidazolium fluoroborate (“HMIMFB”),1-methyl-3-octyl-imidazolium fluoroborate (“MOIMFB”), andbenzyltrimethyl ammonium fluorophosphate (“BTMAFP”).

Ionic liquids are generally commercially available or may be prepared bymethods known in the art. These compounds may be used as is or may befurther purified.

The concentration and amounts of the solutions are chosen such that themolar ratio of the alkylating agent compound to the metal salt isgreater than or equal to the stoichiometric requirement for theparticular alkylation reaction.

The metal halide with a trialkylaluminum solution reaction may beperformed at −10 to 100° C. Useful pressures are 1 to 10 bar.

The metal halide solution with an alkyl magnesium halide or an alkyllithium solution reaction may be performed at −50 to 50 ° C. Usefulpressures are 1 to 10 bar.

In another embodiment of the present invention, there is provided amethod to prepare metal amidinate compounds that are useful sourcessuitable for Atomic Layer Deposition (ALD). The metal amidinatecomposition is an organometallic compound suitable for use as an ALDprecursor having the formula (R¹NCR²NR³)_(n)M^(+m)L¹ _((m-n))L² _(p),wherein R¹, R² and R³ are independently chosen from H, (C₁-C₆)alkyl,(C₂-C₆)alkenyl, (C₂-C₆)alkynyl, dialkylamino, di(silyl-substitutedalkyl)amino, disilylamino, di(alkyl-substituted silyl)amino, and aryl;M=a metal; L¹=an anionic ligand; L²=a neutral ligand; m=the valence ofM; n=0-6; p=0-3; and wherein m≧n. Metal amidinates can be homoleptic orheteroleptic in nature, i.e. may comprise of different amidinate ligandsor a combination of amidinates and other anioinic ligands. Suchcompounds are suitable in a variety of vapor deposition methods, such aschemical vapor deposition (“CVD”), and are particularly suitable foratomic layer deposition (“ALD”). Also provided is a compositionincluding the above described compound and an organic solvent. Such acomposition is particularly suitable for use in ALD and direct liquidinjection (“DLI”) processes.

The method of preparing an organometallic amidinate compound comprisesreacting a metal halide solution with an amidinato lithium solution in amicrochannel device such as a microreactor to produce a metalalkylamidinate compound, wherein the molar ratio of amidinatolithiumcompound to metal halide is greater than or equal to one. In someembodiments the molar ratio is greater than or equal to 2. In someembodiments the molar ratio is greater than or equal to 3.

The metal halide may comprise a Group II through Group VIII metal. Thereare a sufficient number of halogens present in the metal halide to forma neutral compound. Exemplary metal halides include ZnCl₂, GaCl₃, InBr₃,AlCl₃, HfCl₄, ZrCl₄, GeCl₄, SiCl₄, TaCl₅, WCl₆, SbCl₃ and RuCl₃.

The amidinatolithium compound comprises a single amidinato groupcomprising alkyl or aryl or cyclic groups with 1 to 8 carbons. The alkylgroups may be straight chain, branched, or cyclic.

The metal halide solution and the amidinatolithium solution may compriseany solvent which is inert to the reaction between the metal halide andthe amidinato lithium solution and is also inert to any productsresulting from the reaction. The solvents and reagents need to be dry,and deoxygenated. The solvent should be chosen to provide sufficientsolubility for the reaction to proceed. The metal halide solution andthe amidinato lithium solution may use the same or different solvents.Exemplary solvents include, but are not limited to the aforementionedlist.

In some embodiments the metal halide solution is free of solvent, i.e.,the metal halide is already in liquid form and is added “neat”. Theconcentration and amounts of the solutions is chosen such that the molarratio of the amidinato lithium compound to the metal halide is greaterthan or equal to the stoichiometric ratio required for the desiredreaction.

The reaction may be performed at −50 to 50° C. Useful pressures are 1 to10 bar.

In yet another embodiment, a method of preparing an organometalliccompound comprises, reacting a metal halide solution with an alkyl metalsolution in the presence of a tertiary amine, a tertiary phosphine, or amixture of a tertiary amine and a tertiary phosphine in a microchanneldevice such as a microreactor.

In particular the method comprises reacting a metal halide of theformula R_(m)MX_(4-m), with a Group III compound of the formula R⁴_(n)M¹X¹ _(3-n), in the presence of a tertiary amine or a tertiaryphosphine or mixtures of a tertiary amine and a tertiary phosphine in anorganic solvent to provide an alkylmetal compound, wherein each R isindependently chosen from H, alkyl, alkenyl, alkynyl and aryl; M ischosen from a Group IV metal and a Group VI metal; each X isindependently a halogen; each R⁴ is independently chosen from(C₁-C₆)alkyl; M¹ is a Group III metal; each X¹ is independently ahalogen; m=0-3; and n=1-3. The Group IV metal halides and the Group VImetal halides are generally commercially available, such as from Gelest,Inc. (Tullytown, Pa.), or may be prepared by methods known in theliterature. Such compounds may be used as is or may be purified prior touse. It will be appreciated by those skilled in the art that more thanone metal halide, more than one Group III compound, and combinationsthereof may be used.

Exemplary Group IV metals include, but are not limited to, silicon,germanium and tin. Exemplary Group VI metals include, withoutlimitation, tellurium and selenium. M is preferably silicon, germaniumor tin and more preferably germanium. X may be any halogen. Each X maybe the same or different. In one embodiment, m=0. When m=0, a Group IVor Group VI metal tetrahalide is used. In other embodiments, m may be 1,2 or 3.

A wide variety of alkyl, alkenyl and alkynyl groups may be used for R.Suitable alkyl groups include, without limitation, (C₁-C₁₂)alkyl,typically (C₁-C₆)alkyl and more typically (C₁-C₄)alkyl. In oneembodiment, the alkyl groups are bulky alkyl groups. By “bulky alkylgroup” is meant any sterically hindered alkyl group. Such bulky alkylgroups have at least three carbons, there being no particular upperlimit to the number of carbons in such group. It is preferred that thebulky alkyl groups each have from three to six carbon atoms, and morepreferably three to five carbon atoms. Such bulky alkyl groups arepreferably not linear, and are preferably cyclic or branched. Exemplaryalkyl groups include methyl, ethyl, n-propyl, iso-propyl, n-butyl,iso-butyl, sec-butyl, tert-butyl, pentyl, cyclopentyl, hexyl, andcyclohexyl. More typically, suitable alkyl groups include ethyl,iso-propyl, and tert-butyl. Suitable alkenyl groups include, withoutlimitation, (C₂-C₁₂)alkenyl, typically (C₂-C₆)alkenyl and more typically(C₂-C₄)alkenyl. Exemplary alkenyl groups include vinyl, allyl, methallyland crotyl. Typical alkynyl groups include, without limitation,(C₂-C₁₂)alkynyl, typically (C₂-C₆)alkynyl and more typically(C₂-C₄)alkynyl. Suitable aryl groups are (C₆-C₁₀)aryl, including, butnot limited to, phenyl, tolyl, xylyl, benzyl and phenethyl. When two ormore alkyl, alkenyl or alkynyl groups are present, such groups may bethe same or different.

Any of the above alkyl, alkenyl, alkynyl or aryl groups of R mayoptionally be substituted, such as with halogen or dialkylamino. By“substituted” it is meant that one or more hydrogens on the alkyl,alkenyl, alkynyl or aryl group are replaced with one or more halogens ordialkylamino groups.

A wide variety of Group III compounds may be used. Suitable Group IIIcompounds useful in the present invention typically have the formula R⁴_(n)M¹X¹ _(3-n), wherein each R⁴ is independently selected from(C₁-C₆)alkyl; M¹ is a Group IIIA metal; X¹ is halogen; and n is aninteger from 1 to 3. M¹ is suitably boron, aluminum, gallium, indium andthallium, and preferably aluminum. Preferably, X¹ is selected fromfluorine, chlorine or bromine. Suitable alkyl groups for R⁴ include, butare not limited to, methyl, ethyl, n-propyl, iso-propyl, n-butyl,iso-butyl, and cert-butyl. Preferred alkyls include, methyl, ethyl,n-propyl and iso-propyl. In one embodiment, n is 3. Such Group IIIcompounds where n is 3 include trialkylboron, trialkylaluminum,trialkylgallium, trialkylindium and trialkylthallium, withtrialkylaluminum compounds being preferred. In an alternate embodiment,n is 1 or 2. Such Group IIIA compounds where n is 1-2 includedialkylaluminum halides such as dialkylaluminum chlorides. Group IIIcompounds are generally available commercially from a variety ofsources, such as Gelest, or may be prepared by a variety of methodsknown in the literature. Such compounds may be used as is or may bepurified prior to use.

Suitable tertiary amines include, but are not limited to, those havingthe general formula NR⁵R⁶R⁷, wherein R⁵, R⁶ and R⁷ are independentlyselected from (C₁-C₆)alkyl, di(C₁-C₆)alkylamino-substituted(C₁-C₆)alkyl, and phenyl and wherein R⁵ and R⁶ may be taken togetheralong with the nitrogen to which they are attached to form a 5-7membered heterocyclic ring. Such heterocyclic ring may be aromatic ornon-aromatic. Particularly suitable tertiary amines include, but are notlimited to, trimethylamine, triethylamine, tri-n-propylamine,tri-n-butylamine, tri-iso-propylamine, tri-iso-butylamine,dimethylaminocyclohexane, diethylaminocyclohexane,dimethylaminocyclopentane, diethylaminocyclopentane,N-methylpyrrolidine, N-ethylpyrrolidine, N-n-propylpyrrolidine,N-iso-propylpyrrolidine, N-methylpiperidine, N-ethylpiperidine,N-n-propylpiperidine, N-iso-propylpiperidine, N,N′-dimethylpiperazine,N,N′-diethylpiperazine, N,N′-dipropylpiperazine,N,N,N′,N′-tetramethyl-1,2-diaminoethane, pyridine, pyrazine, pyrimidine,and mixtures thereof. Preferred amines include trimethylamine,triethylamine, tri-n-propylamine, triiso-propylamine, andtri-n-butylamine. In one embodiment, the tertiary amine is triethylamineor tri-n-propylamine.

Exemplary tertiary phosphines include, without limitation, those of thegeneral formula R⁸R⁹R¹⁰P, where R⁸, R⁹, and R¹⁰ are independently chosenfrom (C₁-C₆)alkyl, phenyl and (C₁-C₆)alkyl-substituted phenyl. Suitabletertiary phosphines include triethyl phosphine, tripropyl phosphine,tributyl phosphine, phenyl dimethyl phosphine, phenyl diethyl phosphineand butyl diethyl phosphine.

It will be appreciated by those skilled in the art that more than onetertiary amine or tertiary phosphine may be used. Mixtures of a tertiaryamine and a tertiary phosphine may also be used. Such tertiary aminesand tertiary phosphines are generally commercially available from avariety of sources. Such tertiary amines and tertiary phosphines may beused as is or, preferably further purified prior to use.

A wide variety of organic solvents may be used. Typically, such organicsolvents do not contain oxygenated species such as ether linkages, andare preferably free of oxygen. Exemplary organic solvents include, butare not limited to, hydrocarbons and aromatic hydrocarbons. Suitableorganic solvents include, without limitation, benzene, toluene, xylene,pentane, hexane, heptane, octane, decane, dodecane, squalane,cyclopentane, cyclohexane, cycloheptane, and mixtures thereof. It willbe appreciated that more than one organic solvent may be advantageouslyused in the present invention. In an alternative embodiment, thetertiary amine may be used as the organic solvent. Such organic solventsare generally commercially available from a variety of sources, such asAldrich Chemicals (Milwaukee, Wis.). Such solvents may be used as is or,preferably, purified prior to use.

Preferably, such organic solvents are deoxygenated prior to use. Thesolvents may be deoxygenated by a variety of means, such as purging withan inert gas, degassing the solvent in vacuo, or a combination thereof.Suitable inert gases include argon, nitrogen and helium, and preferablyargon or nitrogen.

The specific tertiary amine, tertiary phosphine and organic solvent useddepend upon the particular alkylmetal compound desired. For example, theorganic solvent and tertiary amine may be selected such that they aremore volatile or less volatile than the desired alkylmetal compound.Such differences in volatility provide easier separation of thealkylmetal compound from both the amine and organic solvent. Theselection of the tertiary amine and the organic solvent are well withinthe abilities of those skilled in the art.

In general, the tertiary amine and/or tertiary phosphine is present in astoichiometric amount to the Group IIIA compound. The mole ratio of themetal halide to the Group IIIA compound may vary over a wide range, suchas from 1:0.1 to 1:5, the particular mole ratio being dependent upon thealkylmetal compound desired. Another suitable range of mole ratios isfrom 1:0.5 to 1:2. Mole ratios greater than 1:5 are also expected to beeffective.

The particular alkylmetal compound obtained from the present method canbe controlled by selection of the mole ratio of the metal halide and theGroup IIIA compound, i.e. the number of halogens replaced in the metalhalide compound can be controlled by the number of moles of Group IIIcompound. For example, in the reaction of a Group IV metal tetrahalide(A), such as germanium tetrachloride, with a trialkylaluminum (B), suchas trimethylaluminum, a mole ratio of 1:0.5 (A:B) provides an alkylGroup IV metal trihalide; a mole ratio of 1:1 (A:B) provides a dialkylGroup IV metal dihalide; a mole ratio of 1:1.5 (A:B) provides a trialkylGroup IV metal halide; and a mole ratio of 1:2 (A:B) provides atetraalkyl Group IV metal. Thus, one, two, three or four halogens of themetal halide compound may be replaced according to the present method.

In one embodiment, the Group III compound, tertiary amine and/ortertiary phosphine and organic solvent may be combined in any orderprior to reaction with the metal halide. In a further embodiment, theGroup III compound is first combined with the tertiary amine and/ortertiary phosphine to form an amine-Group III adduct or aphosphine-Group III adduct. Typically, the amine-Group III adduct may beformed at a wide variety of temperatures. Suitable temperatures forforming the adduct are from ambient to 90° C. The metal halide is thenreacted with the amine-Group III adduct to form the desired alkylmetalcompound. It is preferred that the metal halide is added dropwise,either neat or as a hydrocarbon solution, to the amine-Group III adduct.Alternatively, the amine-Group III adduct may be added dropwise to themetal halide, either neat or as a hydrocarbon solution. Suitabletemperatures to form the alkylmetal compound are from ambient to 80° C.Thus, in one embodiment, the present invention provides a method forpreparing alkylmetal compounds comprising reacting a Group III compoundwith a tertiary amine to form an amine-Group III adduct in an organicsolvent that is free of oxygenated species; and reacting the amine-GroupIII adduct with a Group IV metal halide, Group VIA metal halide or amixture thereof in the organic solvent. When a tertiary phosphine isused in the above reactions, a phosphine-Group III adduct is formed.

In another embodiment, the metal halide may be combined with the GroupIII compound and optionally an organic solvent prior to mixing with thetertiary amine and/or tertiary phosphine. The tertiary amine and/ortertiary phosphine and optionally an organic solvent may then becombined with the metal halide-Group IIIA compound mixture usingsuitable mixing zones within the microchannel device or conventionalexternal agitation techniques. Alternatively, the metal halide-Group IIIcompound may be added to the tertiary amine and/or tertiary phosphineand optionally an organic solvent. While not intending to be bound bytheory, it is believed that the transalkylation reaction does not beginuntil the metal halide, Group III compound and tertiary amine arecombined.

Alternatively, the alkylmetal compound may be prepared in a continuousmanner. For example, the metal halide and the Group III compound may beindependently added in a continuous manner to a microchannel reactor andcontacted with a tertiary amine and/or tertiary phosphine in a suitablesolvent, such as an aromatic or aliphatic hydrocarbon. The addition ofthe metal halide and the Group III compound can be controlled by avariety of suitable means, such as by the use of mass flow controllers.In such a continuous process, the desired alkylmetal compound may berecovered, such as by distillation, while the metal halide and Group IIIcompound are being added to the reaction zone. In a further alternative,a mixture of the metal halide and the Group III compound may be combinedwith the tertiary amine and/or tertiary phosphine in a suitable solvent.In such a continuous process, the desired alkylmetal compound may berecovered, such as by distillation, while the metal halide/Group IIIcompound mixture is being added to the reaction zone.

The organometallic compounds may be used as is or suitably purified by avariety of techniques, such as by distillation, sublimation, andrecrystallization. The present method provides organometallic compoundsthat are substantially free of metallic impurities such as aluminum,gallium, indium, cadmium, mercury and zinc. The organometallic compoundsare also substantially free of oxygenated impurities such as etherealsolvents, and preferably free of such oxygenated impurities. By“substantially free” it is meant that the present compounds contain lessthan 0.5 ppm of such impurities. The present organometallic compoundshave a purity of at least 99.99% or alternatively 99.9999% by weight.Specifically, the organometallic compounds of the present inventioncomprise impurity levels by weight of less than 100 ppm to less than 1ppm.

Organometallic compounds with ultra-high purity for electronic materialsapplications can be further purified using microchannel devices. Themicrochannel device can be used to purify the reactants, intermediates,or final products or combinations thereof to achieve ultra-high puritycompounds for electronic applications. The organometallic compounds canbe produced in microchannel reactors as described above, or intraditional reactors including batch stirred tanks, semi-batch,continuous flow stirred tanks, continuous flow tubular reactors,reactive distillation reactors, and other known methods. Ultra-highpurity material for electronic applications is often difficult toachieve via conventional thermal separation methods such as distillationand sublimation, or by mass transfer separation methods such asextraction, absorption and adsorption due to low concentration drivingforces.

Organometallic compounds containing impurities with near boiling points(relative volatility, 0.8<a<1.5, where a=the vapor pressure of theimpurity/vapor pressure of desired pure compound) are especiallydifficult to purify via staged distillation processes with conventionalpacking. The column may require a large number of stages, >50, >100,sometimes >200, or high reflux ratios, >10, >20, sometimes >50, or both,which adds to the investment and operating cost and complexity of theprocess. The microchannel device provides an improved solution to theseproblems. The small channel dimensions generate higher transportgradients to intensify heat and mass transfer, and increased surface tovolume provides higher effective exchange area in a fixed geometry. Bothfactors contribute to more efficient separation (smaller HeightEquivalent Theoretical Plate, HETP) for purification, especiallybeneficial for attaining high purity.

Ultra high purity organometallic compounds can also be produced in amicrochannel device by adsorptive or chemical purification techniquesuch as adduct-purification. A selective adsorbent or adduct-formingLewis base such as an amine, phosphine, or ether can be supported onmicrochannel surfaces, providing very high exchange area to contact theimpurity-containing stream. Other microchannels can be provided for flowof heat transfer fluid for precise temperature control of the device toefficiently regulate and cycle between the adsorption and desorptionsteps.

Separation processes, such as distillation, stripping, extraction, andadsorption, based on microchannel technology provide the enhanced heatand mass transfer required to achieve ultra pure products (ppm, ppb).These separation processes additionally provide the intensification oftransfer stages needed to solve the problem of separating fluid mixtureswith similar boiling points (relative volatility, 0.8<a<1.5) to highpurity levels. Advantageous operating conditions include temperaturesand pressures where one or more of the fluid components is in the liquidphase and capable of undergoing a phase change either to the vapor stateor to an adsorbed state on a sorbent. This can include temperatures from−25° C. to 250° C., and pressures from 0.1 Pa to 10 MPa. Feed impuritylevels can range from 1 ppm up to 10 wt % or even 50 wt % of the fluidmixture.

The organometallic compounds of the present invention are particularlysuitable for use as precursors in all vapor deposition methods such asLPE, MBE, CBE, ALD, CVD, MOCVD and MOVPE. The present compounds areuseful for depositing films containing one or more of Group IV, Group VIor both Group IV and Group VI metals. Such films are useful in themanufacture of electronic devices, such as, but not limited to,integrated circuits, optoelectronic devices and light emitting diodes.

Films of Group IV and/or Group VI metals are typically deposited byfirst placing the desired alkylmetal compound, i.e. source compound orprecursor compound, in a delivery device, such as a cylinder, having anoutlet connected to a deposition chamber. A wide variety of cylindersmay be used, depending upon the particular deposition apparatus used.When the precursor compound is a solid, the cylinders disclosed in U.S.Pat. No. 6,444,038 (Rangarajan et al.) and U.S. Pat. No. 6,607,785(Timmons et al.), as well as other designs, may be used. For liquidprecursor compounds, the cylinders disclosed in U.S. Pat. No. 4,506,815(Melas et al.) and U.S. Pat. No. 5,755,885 (Mikoshiba et al.) may beused, as well as other liquid precursor cylinders. The source compoundis maintained in the cylinder as a liquid or solid. Solid sourcecompounds are typically vaporized or sublimed prior to transportation tothe deposition chamber.

The source compound is typically transported to the deposition chamberby passing a carrier gas through the cylinder. Suitable carrier gassesinclude nitrogen, hydrogen, and mixtures thereof. In general, thecarrier gas is introduced below the surface of the source compound, andpasses up through the source compound to the headspace above it,entraining or carrying vapor of the source compound in the carrier gas.The entrained or carried vapor then passes into the deposition chamber.

The deposition chamber is typically a heated vessel within which isdisposed at least one, and possibly many, substrates. The depositionchamber has an outlet, which is typically connected to a vacuum pump inorder to draw by-products out of the chamber and to provide a reducedpressure where that is appropriate. MOCVD can be conducted atatmospheric or reduced pressure. The deposition chamber is maintained ata temperature sufficiently high to induce decomposition of the sourcecompound. The deposition chamber temperature is from 200 to 1200° C.,the exact temperature selected being optimized to provide efficientdeposition. Optionally, the temperature in the deposition chamber as awhole can be reduced if the substrate is maintained at an elevatedtemperature, or if other energy such as radio frequency (“RF”) energy isgenerated by an RF source.

Suitable substrates for deposition, in the case of electronic devicemanufacture, may be silicon, gallium arsenide, indium phosphide, and thelike. Such substrates may contain one or more additional layers ofmaterials, such as, but not limited to, dielectric layers and conductivelayers such as metals. Such substrates are particularly useful in themanufacture of integrated circuits, opotoelectronic devices and lightemitting diodes.

Deposition is continued for as long as desired to produce a film havingthe desired properties. Typically, the film thickness will be fromseveral hundred angstroms to several tens of nanometers to severalhundreds of microns or more when deposition is stopped.

The following examples are expected to further illustrate variousaspects of the present invention, but are not intended to limit thescope of the invention in any aspect. All manipulations are performed inan inert atmosphere, typically under an atmosphere of dry nitrogen.

EXAMPLES Comparative Example #1

Tetramethylgermane was synthesized according to the following equation:GeCl₄+2(CH₃)₃Al.Pr₃N.→(CH₃)₄Ge+2CH₃AlCl₂.Pr₃N

To 150 g of high boiling linear alkylbenzenes was added under nitrogentrimethylaluminum (40 g, 0.554 moles) in a 3-necked round-bottomedflask. To this was added n-propylamine (79.5 g, 0.554 moles) dropwise atroom temperature. The addition lasted 30 minutes during which period themixture became warm (ca. 50° C.). After the addition was complete andthe mixture was allowed to cool to room temperature, neat germaniumchloride (40 g, 0.186 moles) was added dropwise at room temperature tothe adduct formed. The addition took 1 hour during which time thereaction mixture warmed again to ca. 60° C. After cooling to roomtemperature, the reaction mass was heated to 160 to 170° C. (oil bathtemperature) during which time 20 g of crude product,tetramethylgermane, distilled through a U-tube into a dry ice cooledreceiver. The identity of the product was confirmed by ¹H nmr (—CH₃resonance at 0.1 ppm) and showed it to contain some tripropyl amine(<5%). Yield of crude product was 81.6%. ¹H nmr analysis of theremaining pot residues indicated the presence of more tetramethylgermanethat was not isolated.

Example 1

Tetramethylgermane is synthesized according to the following equation.GeCl₄+2(CH₃)₃AlPr₃N (CH₃)₄Ge+2CH₃AlCl₂Pr₃N

An equimolar solution of trimethylaluminum and n-propylamine is made ina high boiling linear alkylbenzenes solvent under nitrogen. Thetrimethylaluminum/n-propylamine solution and neat germanium chloride areadded continuously at room temperature to the microchannel device. Themicrochannel device provides separate flow paths for the reagents andthe said flow paths communicate with each other in a mixing region inwhich the reagents contact each other, The reagent flows are controlledto maintain a molar ratio of trimethylaluminum to germanium chloride of3. The mixture enters a reaction region in the microchannel deviceleading to alkylation occurring between the reagents. The said reactionregion has a width perpendicular to the direction of flow in the rangeof 1 to 100 micrometers. The said reaction region has a length (in thedirection of the flow) in the range 1 micrometer to 1 meter, the optimumlength to be determined by the kinetics of the alkylation reaction toachieve an adequate residence time (1 second to 10 minutes) that is setby adjusting the flow rates and to offer at least 80% conversion. Thetemperature of the reaction is controlled to within +/−1° C. by the flowof a heat transfer fluid, such as Therminol, in separate flow channelsto the reaction channels within the microchannel device. The reactionproduct stream exits the microchannel reactor and is collected anddistilled at 160-170° C. to yield the desired Me₄Ge product. The purityof the Me₄Ge product as measured by FT-NMR and ICP-AES is expected to be99.9999% pure.

Example 2

High purity trimethylaluminum-tripropylamine adduct was synthesizedusing microchannel device according to the following equation.(CH₃)₃Al+Pr₃N (CH₃)₃Al.Pr₃N Adduct

The microchannel reactor comprising multiple, parallel channelsconstructed of 316 SS with cross-sectional dimensions of approximately1×3 mm and length greater than 1 m was used in preparation of purifiedorganoaluminum—tertiary amine adduct. Each channel of microchanneldevice was in contact with heat exchange zones. A feedstream oftrimethylaluminum (TMA) at room temperature containing 31.6 ppm Si (asdetected by ICP technique) was fed to the continuous flow reactor at 2.5kg/hr. A feedstream of tripropylamine at room temperature was co-fed tothe reactor through a separate injection port at 5.0 kg/hr. The twofeeds were internally mixed in the flow channels. Reactor temperaturewas controlled using cooling oil (40 ° C.) circulated to the reactorheat exchange channels to maintain a steady process outlet temperatureof ˜50° C. The reactor effluent (7.5 kg/hr) was fed to a continuous thinfilm evaporator to purify the adduct. The evaporator surface wascontinuously wiped by a rotating blade and operated at 2 torr and ajacket temperature of 80° C. The purified TMA:Adduct was collected ingreater than 98 wt % yield and sampled for analysis. The ICP analysisshowed the product to have significantly reduced silicon impurity thanthe starting material, as shown by Si=0.7 ppm reduced from 31.6 ppm.

1. A process for preparing metal amidinate compounds of ultra-highpurity comprising: reacting a metal halide solution and anamidinatolithium solution in a microchannel device to yield a metalamidinate compound wherein the resulting compound has the minimum purityrequired for atomic layer deposition processes.
 2. The process of claim1 wherein the purity of the compound is at least 99.99% pure.
 3. Theprocess of claim 1 wherein the metal halide comprises ZnCl₂, GaCl₃,InBr₃, AlCl₃, HfCl₄, ZrCl₄, GeCl₄, SiCl₄, TaCl₅, WCl₆, SbCl₃ and RuCl₃.4. The process of claim 1 further wherein the reaction is performed inthe presence of an ionic liquid solvent.
 5. The process of claim 1further comprising purifying the amidinatolithium solution.
 6. Theprocess of claim 5 wherein the amidinatolithium solution is furtherpurified using a microchannel device.
 7. A method of preparing a metalamidinate compound of ultra-high purity comprising purifying anorganometallic compound comprising impurities in a microchannel deviceto reduce the level of impurities with relative volatility (a) between0.8≦a<1.5 to a level useful in electronic materials applications.
 8. Themethod of claim 7 comprising purifying a metal amidinate compoundcomprising impurities in a microchannel device to reduce the level ofimpurities with relative volatility (a) between 0.8≦a<1.5 to less than 1ppm.
 9. The method of claim 7 wherein the microchannel device furthercomprises a height equivalent theoretical plate (HETP) of less than 5cm.